Hello community.

I would like to ask an question about Apex.
I want to create an function with Apex but I can not imagine how to create.

The function is as following,

When someone sees the data(e.g. Account data), another object data is registered.

Perhaps this is can be realized with Salsforce Shield but I don't wnat to use this option.

If someone knows good way,could you tell me, please?